This invention relates to a pipe piercing fitting and a valve, comprising a housing which can be attached to a pipe, particularly by welding, containing a guide sleeve with a valve stem disposed therein for axial movement, the valve stem carrying a boring tool for piercing the pipe and a valve body for selectively opening or closing a branch connecting nipple communicating with the valve housing.
Published German Patent Application No. DE 2,709,466 discloses a piercing fitting and valve in whose valve casing a nipple is provided for connecting a branch line. The branch can be, for example, a residential connecting line which is connected by the known fitting to a water main. A valve upper part is threaded into the valve casing, and a threaded sleeve and a guide bushing are threaded into the valve upper part so as to be axially displaceable. These two bushings surround the valve stem, and are moved axially with the valve stem toward the pipe when the pipe is pierced and are subsequently fixed axially in the valve upper part by means of a special locking device. The aforementioned component parts are made of metal and contain a number of interengaging threads as well as locking members. This not only results in a correspondingly high manufacturing cost, but also creates a considerable danger of corrosion damage, so that if such valves are placed underground together with underground pipes for an expected long period of use which may be many decades, their operability becomes questionable after only a few years. Between the valve upper part and the valve seat there is a comparatively large free chamber through which the valve stem passes, and from which the branch nipple opens. The valve spindle is guided in the valve upper part, so that overall the valve connection together with the valve upper part and the bushings referred to constitute a considerable length. Due to the comparatively large distance between the valve seat and the valve stem guide sleeve, the valve casing must be made quite stiff in order to prevent damage to the valve seat by the boring tool when the boring is done. Finally, taking into account the large distance between the guide sleeve and the valve seat, a stable configuration must be assured in order to prevent the valve body from lifting off the valve seat and resulting in leakage when external forces act on the valve upper part.
Published German Patent No. DE 3,830,395 discloses a pipe piercing fitting which serves exclusively for piercing a pipe and does not have any valve function. This pipe piercing fitting contains a valve casing into which a branch nipple opens, whereby a cylindrical sleeve is integrated in the casing. The bottom end of the sleeve is positioned in the vicinity of the branch nipple. A boring tool is disposed in the sleeve for axial displacement through a threaded guide. In order to bore into the pipe, a device with a boring spindle is disposed on top of the valve body and is brought into engagement with the boring tool to operate it. After a hole has been bored, the spindle device is removed, and the free end of the casing is closed off with a plug. This pipe piercing fitting cannot readily be used as a valve, inasmuch as neither a valve seat nor a valve head is provided, in order to selectively open or close the flow path between the interior of the pipe and the branch connection.
Further, published German patent application No. DE 3,744,693 discloses a valve piercing clamp comprising a shell with a vertically oriented valve casing integrally formed thereon. This shell is composed, like the pipe, of PVC. The vertical casing contains a stepped bore with a screw thread in which a T-shaped insert of brass is releasably secured. This insert has a lateral branch connection and also, coaxial with the stepped bore, an additional bore at the upper end into which a spindle sleeve can be screwed. A support body for a boring tool is rotatably arranged in an internal thread inside the valve stem sleeve. Also, a spindle extends out the upper end of the spindle sleeve, which when it is rotated moves the boring tool axially via the support body. The valve piercing clamp consists of a number of components, each of which must be sealed against one another, so that a not inconsiderable expense is required for manufacture and assembly. The insert and the spindle sleeve are formed of metal and are thus subject to corrosion, especially when positioned underground, so that there is no assurance of reliable operation of the integrated boring tool and valve over an extended period of service. Finally, this known valve piercing clamp has a substantial height and additional measures are needed in order to prevent damage when the pipe is laid or during subsequent construction operations.